Construction projects often require a metal or wooden pile to be driven into the earth. A number pile driving systems have been developed to assist in driving piles. Common pile driving systems include drop hammers, vibratory hammers, diesel hammers, and cable actuator systems. Pile driving systems often use a fluid such as hydraulic oil or air to transfer energy to the pile.
The present invention is of primary significance when applied to a class of pneumatic pile driving systems adapted to drive relatively small diameter piles, or posts, into the earth. For simplicity, this class of pile drivers will be referred to herein as post drivers, but it should be clear that members other than posts can be and have been driven using these systems.
Post drivers employ a housing, a piston, a chuck member, and a source of pressurized air. Pressurized air causes the piston to move up and down relative to the housing. The piston engages and drives the pile or post as the piston moves up and down. The chuck member is attached to the housing to facilitate the transfer of energy from the piston to the pile.
The chuck member is typically configured to adapt to the size and shape of the pile being driven. For example, wooden posts are driven by a chuck member defining a cylindrical chamber having an inner diameter slightly larger than the diameter of the post. Channel posts are made of bent steel defining a channel, and a chuck member for driving a channel post may have a projection adapted to fit within the channel defined by the post. Post drivers tend to be relatively small and lightweight and may conveniently be used by one or two people.
A special class of piles includes sheet piles. Sheet piles are typically corrugated sheets that are at least partly driven or buried in the ground. Low gauge sheet piles made of plastic or lightweight steel are often used to form an underground barrier or retaining wall. Typically, these low gauge sheet pile are buried by excavating a trench, placing the sheet pile in the trench, and then filling the trench with dirt.
While attempts have been made to develop chuck members in the form of clamps that attach post drivers to sheet piles, these systems have not been effective and are not widely used. One problem with these sheet pile clamps is that the clamp mechanism tends to absorb the energy of the piston; another problem is that the driving loads tend to be asymmetrically applied to the sheet pile, which causes the sheet to flex. Flexing of the sheet pile absorbs energy and may cause the sheet pile to bend, which may ruin the sheet pile.
The need thus exists for systems and methods for allowing post drivers to be effectively used to drive light gauge sheet piles.